Nitride semiconductor light emitting device and method for manufacturing the same

ABSTRACT

Disclosed are a nitride semiconductor light emitting device in which a critical angle is increased by rounding corners of a substrate so as to improve light extraction efficiency due to increase in an amount of light generated from the inside thereof and extracted to the outside, and a method for manufacturing the same. The nitride semiconductor light emitting device includes a buffer layer formed on a substrate, a light emitting structure including a first conductive semiconductor layer, an active layer and a second conductive semiconductor layer, formed on the buffer layer, a first electrode formed on the first conductive semiconductor layer, and a second electrode formed on the second conductive semiconductor layer, wherein the substrate has a light transmitting property, and respective corners of the substrate are rounded so as to have a designated curvature.

This application is a Divisional of co-pending application Ser. No.12/971,721 filed on Dec. 17, 2010, which claims priority to ApplicationNo. 10-2010-0020660 filed in Republic of Korea, on Mar. 9, 2010. Theentire contents of all of the above applications are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a nitride semiconductor light emittingdevice and a method for manufacturing the same, and more particularly, anitride semiconductor light emitting device which improves lightextraction efficiency and a method for manufacturing the same.

2. Discussion of the Related Art

In general, a nitride Light Emitting Diode (LED) has a light emittingregion including ultraviolet ray, blue light, and green light.Particularly, a GaN-based nitride semiconductor LED is applied tooptical devices of blue/green LEDs, and high-switching and high-outputelectronic devices, such as Metal Semiconductor Field Effect Transistors(MESFET) and Hetero junction Field-Effect Transistors (HEMI).

FIG. 1 is a longitudinal-sectional view illustrating a conventionalnitride semiconductor light emitting device.

As shown in FIG. 1, the conventional nitride semiconductor lightemitting device includes a buffer layer 12 on a substrate 11, an n-GaNlayer 13 on the buffer layer 12, an active layer 14 formed in a multiplequantum well structure to emit light, a p-GaN layer 15, and atransparent electrode 16.

Here, after the n-GaN layer 13 is exposed to the outside by selectivelyetching the transparent electrode 16 to the n-GaN layer 13, an n-typeelectrode 18 is formed on the exposed n-GaN layer 13, and a p-typeelectrode 17 is formed on the transparent electrode 16.

The above conventional nitride semiconductor light emitting device has aprinciple that photons are generated by electron-hole recombination atthe active layer 14 between a P/N junction and the photons escape to theoutside of the light emitting device, thereby generating light.

FIG. 2A is a longitudinal-sectional view schematically illustrating afinal shape of the substrate in the conventional nitride semiconductorlight emitting device, and FIG. 2B is a view illustrating extraction oflight generated from the inside of the substrate of FIG. 2A to theoutside.

In order to increase light extraction efficiency of the conventionalnitride semiconductor light emitting device, a nitride semiconductorgrowth technique or a method of changing the structure of the deviceusing a chip process is used. Otherwise, the light extraction efficiencymay be increased through surface treatment of a certain material.

First, if roughness of a p-GaN layer is achieved according to nitridesemiconductor growth requirements, internal quantum efficiency islowered due to diffusion of magnesium (Mg). However, external quantumefficiency may be improved. Further, in order to use roughness of thep-GaN layer, a technical drawback, such as elongation of a cycle ofmultiple quantum wells, may be encountered.

Further, the conventional p-GaN layer having a thickness of 150˜200 nmcannot be uniformly patterned, and thus the thickness of the p-GaN layerneeds to be artificially increased. However, if the p-GaN layer has anincreased thickness through growth, resistance of p-GaN layer isincreased, and current crowding occurs due to the fact that dispersionof current is carried out in the vertical direction rather than in thehorizontal direction, thereby causing an increase in operating voltage.

Although the p-GaN layer having an increased thickness is obtainedthrough growth, the p-GaN layer must have a high-quality surface.However, in order to prevent degradation of the active layer duringgrowing of the p-GaN layer, the p-GaN layer is grown at a lowtemperature. If the thickness of the p-GaN layer grown at a lowtemperature is increased, then the p-GaN layer cannot have ahigh-quality surface and thus the performance of the device is lowered.A doping concentration of magnesium (Mg) used to form the p-GaN layerand growth conditions of the P-GaN layer are factors greatly influencingthe shape of the surface of the p-GaN layer, and thus high precision isrequired when performing a growth process.

Second, regarding to changing the structure of a device using the chipprocess, a part of a sapphire substrate or LED GaN layer is formed to areverse mesa structure so as to prevent generated light from beingconfined therein and lost, as a chip shaping technique. In order to formthe part of the sapphire substrate or LED GaN layer to a reverse mesastructure, wet etching is mainly used and an etching solution of the wetetching is one out of strong acids, such as sulfuric acid, phosphoricacid, and nitric acid, a base, such as potassium hydroxide, or mixturesof at least two thereof. In order to perform wet etching of a nitridesemiconductor compound, a high temperature is required. In terms ofproperties of wet etching, it is difficult to achieve precise controland concentration set, and use of a mixture of phosphoric acid andsulfuric acid, which is mainly used, is dangerous.

Finally, a method of increasing light extraction efficiency of a nitridesemiconductor light emitting device by roughing a transparent conductivefilm, such as ITO, is used. The transparent conductive film is roughedby changing parameters of a deposition process, or wet etching is used.However, this method has a drawback, such as difficulty in verifyingprocess reproducibility.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a nitridesemiconductor light emitting device and a method for manufacturing thesame.

One object of the present invention is to provide a nitridesemiconductor light emitting device in which a critical angle isincreased by rounding corners of a substrate so as to improve lightextraction efficiency due to an increase in an amount of light generatedfrom the inside of the substrate and extracted to the outside, and amethod for manufacturing the same.

To achieve this object and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, anitride semiconductor light emitting device includes a buffer layerformed on a substrate, a light emitting structure including a firstconductive semiconductor layer, an active layer and a second conductivesemiconductor layer, formed on the buffer layer, a first electrodeformed on the first conductive semiconductor layer, and a secondelectrode formed on the second conductive semiconductor layer, whereinthe substrate has a light transmitting property, and respective cornersof the substrate are rounded so as to have a designated curvature.

In another aspect of the present invention, a method for manufacturing anitride semiconductor light emitting device includes forming a bufferlayer on a substrate, forming a light emitting structure by sequentiallystacking a first conductive semiconductor layer, an active layer and asecond conductive semiconductor layer on the buffer layer, performingmesa etching of a selective region of the second conductivesemiconductor layer until the first conductive semiconductor layer isexposed, forming a first electrode on the exposed first conductivesemiconductor layer and a second electrode on the second conductivesemiconductor layer, respectively, lapping and polishing the substrateprovided with the first electrode and second electrode formed thereon;rounding respective corners of the substrate on which the lapping andthe polishing have been completed, and dividing the substrate, thecorners of which are rounded, into respective devices through scribingand breaking processes.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a longitudinal-sectional view illustrating a conventionalnitride semiconductor light emitting device;

FIG. 2A is a longitudinal-sectional view schematically illustrating afinal shape of a substrate in the conventional nitride semiconductorlight emitting device;

FIG. 2B is a view illustrating extraction of light generated from theinside of the substrate of FIG. 2A to the outside;

FIGS. 3A and 3B to FIGS. 5A and 5B are longitudinal-sectional viewsschematically illustrating final shapes of substrates in nitridesemiconductor light emitting devices in accordance with variousembodiments of the present invention, and views illustrating extractionof light generated from the insides of the substrates to the outside,respectively;

FIG. 6 is a longitudinal-sectional view illustrating the nitridesemiconductor light emitting device in accordance with the presentinvention;

FIG. 7 is a flow chart illustrating a method for manufacturing thenitride semiconductor light emitting device in accordance with thepresent invention;

FIG. 8 is a flow chart illustrating a method for rounding corners of thesubstrate in the method for manufacturing the nitride semiconductorlight emitting device in accordance with the present invention;

FIGS. 9A-9E show illustrating light extraction efficiency according toshapes of the substrates in the conventional nitride semiconductor lightemitting device and the nitride semiconductor light emitting devices inaccordance with the embodiments of the present invention; and

FIG. 10 is a graph illustrating light extraction efficiency according toetching shapes of FIG. 9A-9E.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, with reference to the accompanying drawings, a nitridesemiconductor light emitting device and a method for manufacturing thesame will be described in detail.

FIGS. 3A and 3B to FIGS. 5A and 5B are longitudinal-sectional viewsschematically illustrating final shapes of substrates in nitridesemiconductor light emitting devices in accordance with variousembodiments of the present invention, and views illustrating extractionof light generated from the insides of the substrates to the outside,respectively.

In the nitride semiconductor light emitting device in accordance withthe present invention, as shown in FIGS. 3A and 3B to FIGS. 5A and 5B,corners of a substrate are rounded and thus a critical angle isincreased, thereby increasing an amount of light generated from theinside thereof and extracted to the outside and thus improving lightextraction efficiency.

FIG. 6 is a longitudinal-sectional view illustrating the nitridesemiconductor light emitting device in accordance with the presentinvention, and FIG. 7 is a flow chart illustrating a method formanufacturing the nitride semiconductor light emitting device inaccordance with the present invention.

Now, the method for manufacturing the nitride semiconductor lightemitting device in accordance with the present invention will bedescribed with reference to FIGS. 6 and 7. As shown in FIGS. 6 and 7, abuffer layer 112 is formed on a substrate 110, and a light emittingstructure 115 including a first conductive semiconductor layer 120, anactive layer 130 and a second conductive semiconductor layer 140 isformed on the buffer layer 112 (operation S110).

The substrate 110 is made of a light-transmitting material. Although oneembodiment of the present invention uses a sapphire (Al₂O₃) substrate asthe substrate 110, the substrate 110 may be made of a material selectedfrom the group consisting of GaN, SiC, ZnO, Si, GaP, InP, and GaAs, ormay be omitted, as needed.

The buffer layer 112 serves to reduce a difference of lattice constantsbetween the substrate 110 and the light emitting structure 115, and ismade of any one selected from GaN, AlN, AlGaN, InGaN, and AlInGaN at adesignated thickness (for example 150˜1,000 Å). An undoped semiconductorlayer (not shown) may be formed on the buffer layer 112, and the undopedsemiconductor layer may be made of undoped GaN. At least one layer ofthe buffer layer 112 and the undoped semiconductor layer may be presenton the substrate 110, or both of the buffer layer 112 and the undopedsemiconductor layer on the substrate 110 may be omitted.

The light emitting structure 115 may be changed into a p-n junction, ann-p junction, a p-n-p junction, or an n-p-n junction within thetechnical range of the embodiment of the present invention. Further,another material layer may be added to the upper or lower surface ofeach of the respective layers 120, 130, and 140 of the light emittingstructure 115, but the light emitting structure 115 is not limited to astack structure of these layers.

The first conductive semiconductor layer 120 may be made of a materialhaving a compositional formula of InxAlyGal-x-yN (0≦x≦1, 0≦y≦1,0≦x+y≦1). For example, the first conductive semiconductor layer 120 maybe an n-type semiconductor layer made of a material, obtained by bondinga group III element and a group V element, selected from the groupconsisting of InAlGaN, GaN, AlGaN, and InGaN, and the n-typesemiconductor layer is doped with an n-type dopant (for example, Si, Ge,or Sn).

The active layer 130 is formed to a single quantum well structure or amultiple quantum well structure. A conductive clad layer (not shown) maybe formed on the upper surface and/or the lower surface of the activelayer 130. The conductive clad layer may be an AlGaN layer.

The second conductive semiconductor layer 140 may be, for example, ap-type semiconductor layer. The p-type semiconductor layer may beselected from the group consisting of InAlGaN, GaN, AlGaN, and InGaN,and the p-type semiconductor layer is doped with a p-type dopant (forexample, Mg). A third conductive semiconductor layer (not shown) may beformed on the second conductive semiconductor layer 140.

Mesa etching of a selective region of the second conductivesemiconductor layer 140 is performed until the first conductivesemiconductor layer 120 is exposed (operation S120).

A first electrode 161 is formed on the exposed first conductivesemiconductor layer 120, and a second electrode 163 is formed on thesecond conductive semiconductor layer 140 (operation S130).

The lower portion of the substrate 110, which provided with the firstelectrode 161 and the second electrode 163, is polished so as to have adesignated thickness by lapping and polishing (operation S140).

The lower portion of the substrate 110 is ground through lapping, andthe lapped surface of the substrate 110 is smoothed through polishing.Here, the lapping is carried out by Chemical Mechanical Polishing (CMP),ICP/RIE dry etching, mechanical polishing using sapphire particles, orwet etching using as an etching solution a mixing solution including anyone or a combination of at least two out of hydrochloric acid (HCl),nitric acid (HNO₃), potassium hydroxide (KOH), sodium hydroxide (NaOH),sulfuric acid (H₂SO₄) phosphoric acid (H₃PO₄), and a compound(4H₃PO₄+4CH₃COOH+HNO₃+H₃O).

Here, the thickness of the substrate 110 may be as thin as possible.However, if the thickness of the substrate 110 is excessively thin, thesubstrate 110 may warp and be difficult to treat, and thus the thicknessof the substrate 110 is preferably about 20˜400 μm (more preferably50˜150 μm).

Thereafter, corners of the substrate 110 on which the lapping and thepolishing have been completed are rounded (operation S150).

The substrate 110, the corners of which have been rounded, is cut intodevices having a designated chip size through scribing and breakingprocesses (operation S160).

The scribing process may be a laser scribing process or a tip scribingprocess, and is performed from the substrate 110 or from the secondconductive semiconductor layer 140. These post-treatment processes maybe changed within the technical scope of the present invention, but arenot limited to the above-described scribing and breaking processes.

A process of measuring the individual devices during the scribingprocess and the breaking process may be performed.

FIG. 8 is a flow chart illustrating a method for rounding corners of thesubstrate in the method for manufacturing the nitride semiconductorlight emitting device in accordance with the present invention.

As shown in FIG. 8, in order to protect the first electrode 161 and thesecond electrode 163, the surface of the substrate 110 is coated with aphotoresist PR to a thickness of 3 μm or more (operation 151).

Thereafter, hard baking of the substrate 110 coated with the photoresistPR is performed within an oven in a chamber atmosphere of a temperatureof 120° C.

Thereafter, the photoresist RP is selectively patterned through exposureand development processes using a photo mask (operation S152).

Thereafter, photoresist baking using a hot plate is carried out so as toallow the patterned photoresist PR to have a designated slop. Here,although a proper angle of the slope of the photoresist PR is 45°, therange of the angle of the slope of the photoresist PR is not limited.The slope of the photoresist PR is determined by temperature and bakingtime of the hot plate.

Thereafter, after photoresist patterning is carried out using thepatterned photoresist PR as a mask so as to correspond to the size ofthe respective nitride semiconductor light emitting devices, thesubstrate 110 is etched using a dry etching apparatus (operation 153).Here, Inductively Coupled Plasma (ICP) equipment is proper as the dryetching apparatus, and the substrate 110 is etched with a mixture Cl₂and BCl₃ gas.

After the etching of the substrate 110 has been completed, thephotoresist PR is removed using an organic cleaning agent (operationS154). Here, the photoresist applied to protect surface of the device isremoved simultaneously.

Table 1 below compares light extraction efficiency according to shapesof the substrates in the conventional nitride semiconductor lightemitting device and the nitride semiconductor light emitting devices inaccordance with the embodiments of the present invention. Further, FIGS.9A-9E show illustrating light extraction efficiency according to shapesof the substrates in the conventional nitride semiconductor lightemitting device and the nitride semiconductor light emitting devices inaccordance with the embodiments of the present invention.

FIG. 10 is a graph illustrating light extraction efficiency according toetching shapes of FIGS. 9A-9E.

TABLE 1 Embodiment Embodiment Embodiment (FIGS. (FIGS. (FIGS. ShapeConventional 3A and 3B) 4A and 4B) 5A and 5B) Efficiency 100% 127% 386%236%

As shown in Table 1 and FIGS. 9A-9E and 10, if the substrate of thenitride semiconductor light emitting device in accordance with thepresent invention is processed to have a radian (round) shape, thenitride semiconductor light emitting device in accordance with thepresent invention maximizes an amount of light generated from the insidethereof and extracted to the outside, compared with the conventionalnitride semiconductor light emitting device, thereby improving lightextraction efficiency.

The area of the substrate having the rounded corners is equal to thearea of the nitride semiconductor light emitting device.

As described above, a nitride semiconductor light emitting device and amethod for manufacturing the same in accordance with the presentinvention have effects, as below.

First, a sapphire substrate used as a substrate of the nitridesemiconductor light emitting device is processed to have a lens-shapedcross-section, and thus increases a critical angle of light emittingoutwards, thereby improving light extraction efficiency through maximallight extraction.

Second, if a flipchip package is applied, a fluorescent substance isuniformly applied due to a uniform curvature of the substrate.

It will be apparent to those skilled in the art that various modifiedembodiments and variations can be made in the present invention withoutdeparting from the spirit or scope of the inventions. Thus, it isintended that the present invention covers the modified embodiments andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method for manufacturing a nitridesemiconductor light emitting device comprising: forming a buffer layeron a surface of a substrate, wherein the substrate has a lighttransmitting property; forming a light emitting structure bysequentially stacking a first conductive semiconductor layer, an activelayer and a second conductive semiconductor layer on the buffer layer;performing mesa etching of a selective region of the second conductivesemiconductor layer until the first conductive semiconductor layer isexposed; forming a first electrode on the exposed first conductivesemiconductor layer and a second electrode on the second conductivesemiconductor layer, respectively; lapping and polishing the substrateprovided with the first electrode and second electrode formed thereon;rounding respective corners of the other surface of the substrate onwhich the lapping and the polishing have been completed, so as to have adesignated curvature, such that the substrate has a convex lens-shapedcross-section; and dividing the substrate, the corners of which arerounded, into respective devices through scribing and breakingprocesses.
 2. The method according to claim 1, wherein the rounding ofthe respective corners of the other surface of the substrate includes:coating the surface of the substrate with a photoresist, and hard-bakingthe photoresist in order to protect the first electrode and the secondelectrode; selectively patterning the photoresist through exposure anddevelopment processes; performing photoresist baking using a hot plateso as to allow the patterned photoresist to have a designated slope;performing photoresist patterning using the patterned photoresist a maskso as to correspond to the size of the respective nitride semiconductorlight emitting devices, and then selectively etching the substrate usinga dry etching apparatus; and removing the photoresist using an organiccleaning agent when the etching of the substrate has been completed. 3.The method according to claim 2, wherein the dry etching apparatus isICP equipment, and the substrate is etched with a mixture of Cl₂ andBCl₃ gas.
 4. The method according to claim 2, wherein an angle of theslop of the photoresist is 45°, and the slope of the photoresist isdetermined by temperature and baking time of the hot plate.